Method of treating gold and like bearing ores



Patented Aug. 18, 1936 UNITED STATES.

METHOD OF TREATING GOLD AND LIKE BEARING ORES Alfred Leslie Blomfield, Kirkland Lake, Ontario,

Canada No Drawing. Application January 7, 1935, Serial No. 703. In Canada January 12, 1934 2 Claims.

This invention relates to a method of treating ores and more particularly concentrates thereof for the recovery therefrom of gold and like metals.

The cyanide process for the extraction of gold from its ores has long been practiced and is highly developed. In the early practice of the process MacArthur and Forrest found that the use of potash, lime or the like with the cyanide improved the process, as shown in Canadian Patent No. 33,976, issued March 20, 1890. In his Canadian Patent No. 43,524, issued July 7, 1893, Montgomerie shows that the use of sodium oxide or other suitable oxides effects important economies in the operation of the process and in the amount of cyanide consumed, and that the amount of such oxides to be used depends upon the character of the ore under treatment. Since these early days, lime has been extensively used and in Widely varying proportions. When the concentrate of the ores, rather than the ore itself, is under cyanide treatment the amount of lime employed is increased in proportions in accordance with the concentration in the product under treatment of the cyanide-consuming constituents and with the particular process employed in that treatment. Thus lime has been used at the rate of 10, 20, 50, or more pounds per ton of material under treatment as conditions require.

The use of lead or its salts or compounds was perhaps first applied by MacArthur, as shown in his Canadian Patent No. 44,621, granted November 3, 1893, and similarly others have disclosed various specific cyanide treatment processes involving the use of lead salts.

The present invention has as its object the better utilization of lime and the provision of a process in which the use of lime and lead salts is employed in an improved manner in order to provide greater economy of operation, toavoid undue cyanide consumption, to avoid re-precipitation of gold in the agitators, thickeners, etc., and to obtain a higher gold extraction at reduced cost.

While the process may be applied to the ore, it will now be particularly described with respect to its application to concentrates obtained from the ore by flotation or other desired method.

Concentrates from a flotation plant or the like are well washed in, for example, an Oliver filter of well known construction. The washed concentrates are then agitated for an extended period varying from 36 to 50 hours in the presence of an excess of lime which may be equivalent to 60 to 150 pounds per ton of concentrates. The

agitators should be preferablyopen to the atmosphere to insure adequate admission of air at this stage of 'the operation. It has been found that incorporation of a small portion of lead salt, preferably lead oxide, at this stage of agitation in the presence of the excess lime, has the effect of decreasing the necessary time of agitation in the cyanide solution and, at the same time, of substantially reducing the gold values in the final tailings. Two pounds of the lead salt per ton of the concentrate is normally sufficient, and it may be added in successive portions in the several agitators during the agitating period. Cyanide may be added'during the agitation in the presence of the excess lime and added lead salt, or the cyanide need not be added until the required agitation with the lime and lead salt is completed. The agitation, however, must be such as to obtain the eflfect of the combined action of the excess lime and lead oxide on the concentrates. This has the effect of reducing the period of agitation after the cyanide has been added and it substantially facilitates the process, increasing the efliciency of the total gold recovery, thus giving cleaner tailings. It reduces the actual cost of the cyanide treatment and of the chemical reagents used. Furthermore, it largely, if not entirely, eliminates the tendency for the a gold to i e-precipitate during the normal agitating and thickening steps of the process.

The washing of the tailings and other detailed steps of the process may be carried out as in normal well known practice.

The treatment described may be applied directly to the ore, with the necessary reduction in the amount of lime and lead oxide used. The lime may be reduced to but a fraction of that required by the concentrate as will be apparent to those skilled in the art, and as little as 0.2 pound of lead oxide per ton of ore may be used in combination with the lime when treating the ore, although considerably more may be profitably used in some cases. In treating a particular ore containing tellurides it has been found that the addition of lead oxide up to 1.5 pounds per ton of ore with about 7 pounds of lime has a decidedly beneficial effect in recovering the telluride gold content, and in raising the sulphides by flotation from the cyanide tails, despite the normal depressing effect of lime on the sulphides.

In the treatment of the ore after grinding im-- proved results are obtained by introducing to and maintaining in the ore throughout the agitating operations active lime which is always available to take the place of lime removed from soluon by the eactions in the process. Whilethe specific reason for the'advantage of maintaining this extra lime is not thoroughly understood, "it

appears that the. ionization caused by the lime going into solution has an influence upon the reactions taking place. It appears that this 'ex- '7 ltra lime must be present to immediately replace lime consumed and removed as such "from solution arid that protective alkalinity c'aused by other reagents which maybe-present is not sufiicient. "This is accomplished by introducing to the ore 1 during the agitating operations such amounts of lime as will always maintain lime in excess of Q that necessary for substantial saturation with lime. This treatment is sometimes more effective when the grinding is done withoutcyanide addi-- tion, although it may be carried out in the presence of cyanide additions. It lessens the precipitating effect on carbon which is prevale'nt in some ores. v 7

It will be observed that the invention is directed tothe improvement of the specific method of treating gold ores and particularly those 0on1 taining :tellurides, with a view to obtaining a; 7 higher gold'recovery and ma shorter period of time, Aspreviousl'y stated, lime and lead salts have been previously widely used but the partreated concentratesin the presence of cyanide.

:ZQA process of recovering gold as definedin ticular way of using'thelime mine agitation f the raw ore and the combined use of lime and lead salts in the treatment of the concentrates and mainly at a point preparatory to cyanide treatmerit give results which-yield'greater eiiiciency of operation and of recovered'gold. The duration of time the material is in process of operation is trates with water, adding thereto lime'at' the rate 15 V V of 60 to 150 pounds per ton of concentrates, agitating the 'pulp in thepresence of said lime,'in-

an important consideration and these improvecorporating therein lead oxide in the] proportion of substantially 2 pounds perrton ofconcentrates.

during said agitation andthen agitating the so-v claim l, wherein said lead oxide is added in successive small portions during the'continued agita- I excess lime. V r v ALFRED LESLIE BLOMF'IELD.

' tion of the concentrates in the presence of said 25 

